Most likely the "rubber" in the headphones that went gummy was a
Urethane product.
A known and widely found failure of Urethane is to take up humidity,
even office humidity, and fail in a sticky gummy mess.
This has plagued the tape industry since about 1975 to 85 or later, and
was from the introduction of back coated tapes where the coating "glue"
was urethane adhesive. I have made my living for the last 7 plus years,
studying urethane failures, and doing remediation on tapes suffering
this "sticky shedding syndrome" Tape can be baked to reverse the sticky
condition. This may or may not help with other sticky polymers, and not
likely after they are gummy all the way through.
At least tape bakes out stable long enough to transfer its content to
other media, or to digitize the content.
Many in the technical trades or hunters have found the gummy state of
old foam in a carrying case for their tools, shotgun or rifle. Again,
this is Urethane foam rot. One of the examples that it is not always
"better living through chemistry" to quote and old ad.
Tapes are baked for one month at 54 degrees C, which is about 121
degrees F. These are one inch by 14 inch reels having as much as 12,500
feet or more usually, 9200 feet of tape upon them. Smaller affected
material can be baked as short as 48 hours for a 7 inch reel of music
tape. Some tapes did not use urethane, but no one knew what Urethane
would do over time, when it was introduced.
-Stuart Rohre
K5KVH
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